Cancer in twin pairs discordant for smoking: The Nordic Twin Study of Cancer
Menée à l'aide de données de l'étude "NorTwinCan" portant sur des jumeaux n'ayant pas le même comportement tabagique (durée médiane de suivi : 27 ans), cette étude analyse l'association entre le tabagisme et le risque de cancer de l'oesophage, du rein, du larynx, du foie, du poumon, de la cavité buccale, du pancréas, du pharynx ou de la vessie (7 379 cas)
The discordant twin pair study design is powerful to control for familial confounding. We employed this approach to investigate the associations of smoking with several cancers. The NorTwinCan study combines data from the Danish, Finnish, Norwegian, and Swedish twin and cancer registries. Follow-up started when smoking status was determined and ended at cancer diagnosis confirmed by information in the cancer registry, death, or end of follow-up. We classified the participants as never (n=59,093), former (n=21,168) or current (n=47,314) smokers. We pooled data from twin pairs where one co-twin was diagnosed with any of the following tobacco-related cancers: esophagus, kidney, larynx, liver, oral cavity, pancreas, pharynx, or urinary bladder, while their co-twin had none of those. Lung cancer was included in further analysis. We used Cox regression allowing for pair-specific baseline functions to estimate hazard ratios (HR) with 95% confidence intervals (CI). For tobacco-related cancer sites, we recorded 7379 cases during median 27 years of follow-up. The analyses based on individual twins showed that former (HR 1.31, 95% CI: 1.17-1.48) and current (HR 2.14 (1.95-2.34)) smokers are at increased risk to develop one of those cancers, compared with never smokers. Among 109 monozygotic twin pairs discordant for cancer and smoking, the HR was 1.85 (95% CI: 1.15-2.98) among current smokers and 1.69 (1.00-2.87) among former smokers when compared with their never smoking co-twin. Thus, associations of smoking with several cancers were replicated for discordant identical twin pairs. Analyses based on genetically informative data provide evidence consistent with smoking causing multiple cancers.